The Doctrine of First Sale (DoFS) is an exception to copyright law that enables an end user to sell or give away a copy of copyrighted work. The DoFS is accepted by copyright holders partially because transfer of physical objects from one person to another is inherently bound by the laws of physics, essentially limiting the speed by which the object can be transferred from one person to another.
For this same reason, there is opposition to apply the DoFS to the virtual world such as digital copyrighted work. With digitized copyrighted work, the transfer from one person or location to another only takes the push of a button, thus increasing the speed by which the transfer can occur.